Radio frequency power amplifier and wireless communication device including the same

Abstract

To provide a radio frequency power amplifier that realizes a favorable high-frequency characteristic without using an isolator and also achieves low power consumption. The radio frequency power amplifier includes: a power amplifier which amplifies a radio frequency signal; a voltage supplying unit which supplies a collector voltage to the power amplifier; a current supplying unit which supplies a bias current to the power amplifier; and a bias current detecting unit which detects the bias current. The voltage supplying unit has a control unit which sets the power supply voltage at: a first voltage when the detected bias current is lower than a bias-current reference value; and a second voltage lower than the first voltage when the detected bias current is higher than the bias-current reference value.

1 . A radio frequency power amplifier comprising:
 an amplifying unit configured to amplify a radio frequency signal;   a voltage supplying unit configured to supply a power supply voltage to said amplifying unit;   a current supplying unit configured to supply a bias current to said amplifying unit; and   a detecting unit configured to detect the bias current,   wherein said voltage supplying unit includes a control unit configured to set the power supply voltage at: a first voltage when a value of the detected bias current is equal to or lower than a threshold; and a second voltage lower than the first voltage when the value of the detected bias current is higher than the threshold.   
     
     
         2 . The radio frequency power amplifier according to  claim 1 ,
 wherein the threshold indicates a bias-current reference value in association with a value of an output power of said amplifying unit, the bias-current reference value corresponding to an ideal output load on said radio frequency power amplifier.   
     
     
         3 . The radio frequency power amplifier according to  claim 2  further comprising:
 a memory which stores a plurality of bias-current reference values in association with a plurality of values of the output power, the bias-current reference values corresponding to the ideal output load on said radio frequency power amplifier; and 
 an obtaining unit configured to obtain the value of the output power of said amplifying unit, 
 wherein said control unit is configured to compare the bias-current reference value stored in said memory in association with the obtained value of the output power of said amplifying unit and the value of the bias current detected by said detecting unit, and to set the power supply voltage at: the first voltage when the value of the bias current detected by said detecting unit is equal to or lower than the bias-current reference value stored in said memory; and the second voltage when the value of the bias current detected by said detecting unit is higher than the bias-current reference value stored in said memory. 
 
     
     
         4 . The radio frequency power amplifier according to  claim 1 ,
 wherein the second voltage is a voltage for causing an adjacent channel leakage ratio of said radio frequency power amplifier to be lower than a predetermined value when the value of the detected bias current is higher than the threshold.   
     
     
         5 . The radio frequency power amplifier according to  claim 1 ,
 wherein the first voltage is a voltage for causing the adjacent channel leakage ratio of said radio frequency power amplifier to be lower than the predetermined value regardless of the value of the detected bias current.   
     
     
         6 . The radio frequency power amplifier according to  claim 1 ,
 wherein, when the power supply voltage is set at the first voltage and the value of the detected bias current becomes higher than the threshold, said control unit is configured to change the power supply voltage from the first voltage to the second voltage.   
     
     
         7 . The radio frequency power amplifier according to  claim 1 ,
 wherein, when the power supply voltage is set at the second voltage and the value of the detected bias current becomes equal to or lower than the threshold, said control unit is configured to change the power supply voltage from the second voltage to the first voltage.   
     
     
         8 . The radio frequency power amplifier according to  claim 1 ,
 wherein said control unit is further configured to control the power supply voltage according to the output power of said amplifying unit.   
     
     
         9 . The radio frequency power amplifier according to  claim 8 ,
 wherein, when the output power of said amplifying unit is higher than a predetermined power, said control unit is configured to set a first upper-limit voltage as the first voltage, and   when the output power of said amplifying unit is equal to or lower than the predetermined power, said control unit is configured to set, as the first voltage, a second upper-limit voltage lower than the first upper-limit voltage.   
     
     
         10 . The radio frequency power amplifier according to  claim 9 ,
 wherein, when the output power of said amplifying unit is higher than the predetermined power, said control unit is configured to set a voltage equal to or higher than the second upper-limit voltage as the second voltage.   
     
     
         11 . The radio frequency power amplifier according to  claim 3 ,
 wherein said obtaining unit is connected to said amplifying unit and configured to detect the output power of said amplifying unit.   
     
     
         12 . The radio frequency power amplifier according to  claim 3 ,
 wherein said obtaining unit is configured to estimate the output power of said amplifying unit, from a power of the radio frequency signal received by said power amplifying unit and an amplification gain of said power amplifying unit.   
     
     
         13 . The radio frequency power amplifier according to  claim 1 ,
 wherein said amplifying unit has:   a first amplifying element which amplifies the radio frequency signal in a first frequency band;   a second amplifying element which amplifies the radio frequency signal in a second frequency band different from the first frequency band; and   a bias line provided in common to said first amplifying element and said second amplifying element so that the bias current is supplied to each of said first amplifying element and said second amplifying element.   
     
     
         14 . The radio frequency power amplifier according to  claim 13 ,
 wherein each of said first amplifying element and said second amplifying element is a transistor,   said amplifying unit further has:   a first line connected to a collector of said first amplifying element and used for transmitting the radio frequency signal amplified by said first amplifying element;   a second line connected to an emitter of said first amplifying element;   a third line connected to a collector of said second amplifying element and used for transmitting the radio frequency signal amplified by said second amplifying element; and   a fourth line connected to an emitter of said second amplifying element, and   said bias line is arranged so as not to overlap with any of said first to fourth lines.   
     
     
         15 . The radio frequency power amplifier according to  claim 1 ,
 wherein said amplifying unit has:   an m number of amplifying elements connected in multiple stages, m being an integer of at least 2; and   an m number of bias lines for supplying bias currents to said m number of amplifying elements, respectively, and   said detecting unit is configured to detect the bias current supplied to at least one of said m number of bias lines.   
     
     
         16 . The radio frequency power amplifier according to  claim 15 ,
 wherein said detecting unit is configured to detect the bias current supplied to a bias line corresponding to an amplifying element of a final stage out of the multiple stages.   
     
     
         17 . The radio frequency power amplifier according to  claim 15 ,
 wherein said detecting unit is configured to detect the bias currents supplied to said m number of bias lines, in association with said m number of amplifying elements, respectively.   
     
     
         18 . The radio frequency power amplifier according to  claim 17 ,
 wherein said control unit is further configured to control the power supply voltage, according to a difference between: the bias current supplied to an amplifying element, out of said m number of amplifying elements, of an i-th stage where 1≦i≦m-1; and the bias current supplied to an amplifying element, out of said m number of amplifying elements, of a j-th stage where i<j and 2≦j≦m.   
     
     
         19 . The radio frequency power amplifier according to  claim 1 , further comprising:
 a current control transistor for controlling the bias current; and   a temperature compensation circuit for performing temperature compensation on said current control transistor and said amplifying unit.   
     
     
         20 . A wireless communication device comprising
 the radio frequency power amplifier according to  claim 1 .